MCBG Session 18 - Three Parent Babies

Question 1

What theory explains how mitochondria came to be a intracellular organelle?

Answer 1

• Endosymbiotic theory - ancestral eukaryotes lived symbiotically with prokaryotes which were engulfed to become the mitochondria.
• This manifests due to the mitochondria having replication patterns, rRNA and DNA more similar to prokaryotes than eukaryotes and they don’t have the full complement of genes to be self-sustaining organisms.

Question 2

What is the main function of the mitochondria?

Answer 2

The site of anaerobic cell respiration. It is the powerhouse of the cell and produces ATP to release energy.

Question 3

Which tissues or organs would you expect to be more affected by mitochondrial disease and why?

Answer 3

High energy deman organs: heart, brain, liver, kidneys, nerves (need to maintain ionic gradient)

Question 4

What symptoms would you expect in mitocondrial disease?

Answer 4

The more common symptoms are:

• Poor growth
• Loss of muscle co-ordination, muscle weakness
• Neurological problems, seizures
• Heart, liver or kidney disease

Question 5

Mitochondrial disease is rare. Looking at the symptoms, why does the clinical presentation of mitochondrial disease cause difficulties to doctors?

Answer 5

• None of the hallmark symptoms of mitochondrial disease - muscle weakness, exercise intolerance, hearing impairment, ataxia, seizures, learning disabilities, cataracts, heart defects, diabetes and stunted growth - are unique to mitocondrial disease.
• However, a combination of three or more of these symptoms in one person strongly points to mitochondrial disease, especially when the symptoms involve more than one organ system.

Question 6

Symptoms of mitochondrial disease can range from mild to severe in families with a specific mutation in one mitochondrial-encoded gene. How can this be explained?

Answer 6

• Depending on how severe the mitochondrial disorder is, the disease can range from severe to mild.
• Hence it depends on the distribution of the mutated mitochondria and the rate of production of mitochondria in different tissues, especially with younger children who are developing.

Question 7

Mitochondrial disease affects more than the individual. Why does it cause difficulties to more than affected individual?

Answer 7

• Female affected - ability to have children, affect relationships with future partners.
• Partner of affect individual - financial implications as may not be able to work to support family, increased care needs.

Question 8

Why is mitochondria replacement therapy so controversial?

Answer 8

• Mitochondrial donation involves modification of the germline, and hence such modifications would be passed on to subsequent generations.
• This could also lead down a slippery slope towards genetically modified and designer babies, whereby certain traits are “fixed” or “changed”.
• Using human embryos in vitro research is also controversial, as embryos are created specifically for research and the financial compensation of egg donors.